Effect of Specimen Collection and Storage on Blood Glucose and Lactate Concentrations in Healthy, Hyperthyroid and Diabetic Cats

The objective of this study was to compare and investigate differences in glucose and lactate concentrations in sodium fluoride/potassium oxalate (NaF/Ox) plasma and serum in healthy cats and cats with metabolic disease. Glucose and lactate concentrations were determined in routinely processed serum and NaF/Ox plasma obtained from healthy (n=30), hyperthyroid (n=27) and diabetic (n=30) cats, and in samples from 6 healthy cats stored at 25 degrees C or 4 degrees C for 0, 1, 2, 4, or 8 hours. The packed cell volume (PCV) of blood collected in NaF/Ox was compared with that of blood collected in EDTA. Mean glucose concentration was significantly (P<.05) lower in NaF/Ox plasma than in serum in all groups of cats, by 0.7-2.5 mmol/L (11-45 mg/dL); the difference was greater in hyperthyroid and diabetic cats. In vitro, only serum stored on the clot for >/= 1 hour at 25 degrees C had significantly lower glucose and higher lactate concentrations. The PCV of NaF/Ox-anticoagulated blood was lower that that of EDTA-anticoagulated blood, by 7.0% +/- 1.4% (P<.01). In conclusion, collection of feline blood in NaF/Ox was necessary to prevent in vitro increases in lactate concentration; however, NaF/Ox artifactually decreased plasma glucose concentration because of RBC shrinkage. The PCV should not be determined on blood collected in NaF/Ox.